Filtration process

ABSTRACT

A method of phase separation using ferromagnetic materials. A mixture of phases is treated with particles or granules of ferromagnetic material so that one of the phases is preferentially absorbed or collected onto or into the particles or granules. The particles or granules of the ferromagnetic material together with the absorbed or collected phase may then be recovered from the remainder of the mixture using magnetic means.

This is a division of application Ser. No. 138,679 filed Apr. 29, 1971,now U.S. Pat. No. 3,890,224.

This invention is concerned with an improved method of phase separation.

Conventional means of separating the constituent phases of a mixturesuch as, for example, allowing a mixture of liquids to separate intodiscrete layers and then removing one layer from contact with the otherlayer, or by separating a solid from a liquid by filtration, can beextremely inefficient in certain instances. For example, emulsions andcolloidal solutions are particularly difficult to separate out intotheir constituent phases. Also in instances where a second phase forms aminor proportion, or even a mere trace proportion of the whole of themixture, such as when an oil slick is present on the surface of seawater, efficient removal of such a proportion is particularly difficult.It is also difficult to remove solids such as occur in water supplies orsewage effluents, or gelatinous precipitates, such as hydrated metalhydroxides, from aqueous media.

We have now found a method whereby different phases in a system may beseparated, one from another, in an extremely efficient manner.

Accordingly we provide a process of phase separation, said processcomprising the treatment of a mixture of phases with ferromagneticmaterial in particulate or granular form whereby at least part of onephase of the said mixture is absorbed or collected into or onto saidparticulate or granular material and the separation by magnetic means,of said particulate or granular material, together with said absorbed orcollected portion of the mixture, from the remainder of the mixture.

Although inorganic ferromagnetic materials such as, for example,gamma-iron oxide or magnetite, are of use in certain applications suchas, for example, the use of ferromagnetic materials in reducing theentrainment of water in air, in many applications it is preferred to usea synthetic polymer comprising ferromagnetic material.

One class of suitable polymers for use in a given multi-phase mixture inwhich at least one of the phases is a liquid are those which arepreferentially wetted by a liquid phase of the mixture. The wettabilityof polymers, or the critical surface tension is defined as being thelowest surface tension a liquid in contact with the polymer can have andstill exhibit a contact angle greater than zero. Values for the criticalsurface tension of a number of polymers are given in "Polymer Handbook"(Edited by J. Brandrup and E. H. Immergut, published by J. Wiley & SonsInc., 1966) Section III, pages 113 - 114. This may be used as a guide tothe selection of polymers which will be preferentially wetted by aliquid but is, of course, not limiting and many other suitable polymershave been described in the art. The chemical constitution of thepolymers is not critical except insofar as the polymer should haveadequate insolubility as well as mechanical and chemical stability inthe mixture; the main criterion for selection is wettability. Thus,suitable polymers for use in our invention can be chosen from all typesof polymers such as both addition and condensation polymers; furthermoresuch polymers may be grafted onto the surface of a different polymerparticle in order to achieve the desired wetting properties.

A second class of suitable polymers are those which will preferentiallyabsorb one of the phases of the mixture. Suitable polymers are thosewhich will swell in good solvents for the polymer and will not do so innon-solvents. A table useful in the selection of suitable polymers ofthis class is to be found in "Polymer Handbook" referred to above,Section 17, pages 185 - 234. Phase separation may thus be achieved ifthe constituent phases of the mixture comprise a good solvent and anon-solvent for a selected polymer. Furthermore, heating such polymers,when in a swollen state, can in favourable situations cause contractionof the structure and exudation of the absorbed solvent. Certain of thesepolymers may be cross-linked. The cross-linking of such polymers can beof two types. In one type the cross-links are randomly distributedthroughout the polymer network. In another type, for example withpolymers of the shell type, the polymer chains are insolubilised by theends of their chains being grafted on to an impervious, inert supportingcore by methods known in the art. The chain mobility in suchwhisker-like structures is much greater than in the randomlycross-linked polymers and favours thermal contraction of the chainsprovided they are in a rubber-like state.

Suitable polymers may be of natural or synthetic origin and of the typesreferred to as condensation or addition polymers, homo polymers orrandom, block or graft copolymers.

Suitable polymers are, for example, polystyrene, copolymers of styreneand polyesters, polyesters, methyl methacrylate polymers and copolymerse.g. with the ethylene glycol dimethacrylate, phenol formaldehyderesins, polyvinyl chloride, polyethylene, polyamides. These polymers andcopolymers are normally hydrophobic in character and therefore findapplication mainly in separating hydrocarbons from aqueous phases suchas for example separating oil slicks from water and also as filter aidsin non-aqueous systems.

Other polymers are, for example, polyvinyl alcohol, urea formaldehyderesins and melamine formaldehyde resins. These polymers are normallyhydrophilic and find main application as filter aids in aqueous systemsand in separating traces of a polar phase from a non-polar phase.

The efficiency of the process also depends on the size, sizedistribution and shape of the polymer particles or granules. The greaterthe external surface area of the particles or granules the greater theamount of material which will be collected onto the surface and also themore rapidly will the process occur.

The size range of particles of use in our invention is not narrowlycritical and depends on the conditions of use. For example we have foundthat relatively coarse particles of from 500 to 5000 microns overalldiameter are best for certain applications such as, for example removingoil slicks from the surface of the sea especially in windy weather. Foruse as filter aids smaller particles are preferred. Preferably theaverage size of the particles or granules is from 0.1 to 500 micronsoverall diameter, more preferably from 0.5 - 40 microns.

The amount of material absorbed or collected in or on a given weight ofpolymer particles or granules will also be increased by the presence ofvoids in the particles or granules. Such voids may be predominantlyinterconnected with the particle surface; such particles are calledreticulated or retiporous particles or granules. Alternatively the voidsmay occur predominantly as completely sealed voids; such particles aretermed vesicular particles or granules. Furthermore the particles may beof a heterogeneous structure for example made up of layers such as ashell of one polymer grafted on and around a particle, formed from adifferent polymer with or without voids. The vesicules are of particularuse in adjusting the specific gravity of particles. Particles may be ofregular shape but it is preferred that they be of irregular shape suchthat they cannot pack closely and that they have a low packing densityand increase the volume of the void space. Such particles areparticularly useful for the separation of solid/liquid and solid/gasphases.

The particles or granules together with the absorbed or collectedmaterial may be removed from the residual phase of phases by anysuitable physical means, such as filtration, centrifugation orsedimentation, or the like.

However, although such means are satisfactory, they are relatively timeconsuming, when the particles or granules are in the preferred sizerange. We have now found that small particles or granules of certainpolymers containing ferromagnetic materials and an absorbed phase may beremoved very efficiently from the residual phase or phases by use of amagnetic field.

Accordingly we provide a process of separating phases of a mixture onefrom the other which process comprises treating the mixture of phaseswith a particulate or granular ferromagnetic synthetic polymericmaterial so as to absorb or collect at least part of one phase of themixture into or onto said particulate or granular material andseparating said particulate or granular material together with theabsorbed or collected portion of the mixture by magnetic means.

The ferromagnetic particles, with their absorbed material may be removedfrom the other phase (or phases) by known means described in the art,such as, for example, by direct removal with a magnetic separator or bymagnetising the particles so as to induce flocculation annd resultantrapid settling of the particles together with absorbed material. Thus inthe instance of a two phase system wherein one of the phases has beenabsorbed on the ferromagnetic particles and the residual phase is aliquid, the residual supernatant liquid can then be decanted from thesettled floc. The particles can remain magnetised during the process ofabsorbing the phase, the increased void volume of such magneticallyflocculated particles is advantageous as it provides additional voidspace for retention of the absorbed material.

Suitable ferromagnetic polymers have a ferromagnetic componentincorporated either wholly or partially within a layer of polymer.Subsequent layers of the same or different polymers may be grafted on oradded. The ferromagnetic components can, for example, be either a softferrite, a hard ferrite or a material which exhibits reversiblemagnetism such as gamma-iron oxide, magnetite or chromium dioxide. Theferromagnetic material must obviously be of a particle size smaller thanthe polymer particles to be prepared. Certain suitable ferromagneticmaterials such as for example mill scale are very expensive to grind tothe desired degree of fineness. Magnetic iron oxides, by contrast, aresimple to prepare as fine powders and are therefore convenient to usewhere a reversible ferromagnetic polymeric material is required. Thegreater ease of dispersion of an unmagnetised, reversible ferromagneticmaterial, as compared to a hard ferrite which becomes magnetic whenground to the required degree of fineness, is advantageous when thematerial is to be incorporated within polymers.

The ferromagnetic polymeric materials used in this invention may beprepared by the normal methods known in the art. Suitable methods whichmay be mentioned include the following. The magnetic material may bedispersed in a monomer or monomer mixture which may then be polymerisedto give the required particles. Another method is to compound a mixtureof a polymer and magnetic material together by a milling operation. Thefinely ground mixture may then be granulated to give material of therequired size range. In yet another method magnetic material may bedispersed in a solution of liquid polymers which may then becross-linked in a curing process. Another method is to deposit a polymeronto magnetic material by polymerisation from the vapour phase by anysuitable method known in the art. A polymer may also be precipitatedfrom a solution onto a dispersion of magnetic particles so as toencapsulate them. Methods for encapsulation are known in the art.

The material absorbed or collected onto the particles or granules may berecovered or removed by simple physical or chemical means. For example,the material may be removed by washing, pressing, distillation or bysolvent extraction. In some instances, the absorbed material can bepartially removed by heating the polymer particles so as to induceshrinkage and exudation of absorbed material. The recovered particles ofgranules may be reused.

There are many situations where it is required to remove very smallamounts of finely divided, or gelatinous particulate matter such asclays and organic matter from for example, surface water supplies orfrom effluents from sewage treatment plants. One such situation relatesto the desalination of water supplies by ion exchange processesutilising counter-current, reverse flow, regeneration procedures. Theefficiency of such processes relies on the development of aconcentration gradient within the bed which must not be destroyedbetween successive regeneration and absorption cycles. Consequentlyback-washing of the bed, which is required to remove accumulatedparticulate matter, must be infrequent and prefiltration of the feedwater is usually essential to reduce the rate of clogging of the ionexchange bed. When because of adverse kinetics as for example in theso-called Sirotherm process of water desalination using thermalregeneration of ion exchange resins, it is desirable also to operate anion exchange fixed bed process with resins having the smallest possibleparticle size (e.g. 50 - 100 mesh as compared with the more usual 20 -50 mesh standard resins) prefiltration is an essential requirement forsuccessful operation to reduce clogging of the bed and distributors. Oneobject of this invention is therefore to provide an improvedprefiltration process for such applications. In other situations, forexample, the treatment of raw sewage itself, the separation of hydrousmetal hydroxides in hydrometallurgical operations or in chemicalprocessing, the concentration of suspended solids is much higher.

In all these instances direct filtration of the suspension is often notpractical as the result of rapid blinding of the pores of the filtermedium by the finely divided or gelatinous material. One known procedurefor increasing filtration rates in such situations is to first precoatthe filter medium with a filter aid -- i.e. a chemically inert solidhaving a low packing density (e.g. diatomaceous earth) before startingthe filtration. In addition to forming a precoat it is also oftenadvantageous to continue to add small amounts of filter aid to the feedso as to maintain the porosity of the accumulation of filter cake ("bodyfeed" technique). The bed of particles provides an incompressible layerof high porosity and permits rapid filtration until the accumulation ofparticulate matter within the voids of the filter and blocks the layer.When the concentration of suspended matter is very low (e.g. about 10ppm), as in some water supplies, this technique is economically feasibleeven though the filter aid must be discarded along with the filter cake.However, when the concentration of suspended solids is high, thenecessary discarding of the filter aid often makes the processuneconomic.

We have now found that our invention will allow for the easyregeneration of the phase separation aid.

Accordingly we provide a process of separating the phases in a mixturecomprising suspensions of particulate matter in a liquid medium whichprocess comprises firstly precoating a filter medium with a layer offine particles or granules of a wettable ferromagnetic material;secondly passing said mixture, optionally in admixture with furtherferromagnetic material, through the precoat layer on the filter mediumso as to separate the particulate matter and ferromagnetic material fromthe liquid phase; thirdly separating said ferromagnetic material fromthe particulate matter by magnetic means.

The ferromagnetic material separated and recovered by the above processmay be reused in phase separation processes, thus leading to a reductionin filter aid costs. In instances where it is desired to recover theparticulate matter, for example in chemical processing or mineralrecovery, the ease of separation of the ferromagnetic filter aid isadvantageous. Preferably the ferromagnetic material is a syntheticferromagnetic polymer.

The selection of suitable polymers is not narrowly critical and can bebased on the criterion of wettability as set out hereinbefore. Thepolymer should also be insoluble in the liquid medium used.

For use in polar media, for example water, typical polymers of use inour process are ferromagnetic particles incorporated wholly or partiallywithin, for example, polyvinyl alcohol, urea formaldehyde resins andmelamine formaldehyde resins.

Preferably the specific gravity of the ferromagnetic polymeric materialshould be such that the settling rate of the unmagnetised filter aid iscomparable with the settling rate of the solid phase to be removed.Adjustment of the specific gravity is achieved by methods well known inthe art, for example, for the production of vesicular particles.

We have found that shell grafted polymers are of particular use in thisaspect of our invention especially if the reactive shell contains groupssuch as polyelectrolytes which will cause flocculation of the fineparticles of suspended solid phase to be separated.

Suitable shell grafted polymers comprising polyelectrolytes are, forexample, particles comprising an inert core consisting of polyvinylalcohol or urea formaldehyde resin grafted with a shell of polyacrylicacid, polyacrylamide or polymethylacrylate or polymers derived fromquaternised amino monomers.

The separation of the solid phase from the ferromagnetic particles maybe accomplished by firstly dispersing the filter cake in a small amountof a suitable liquid by known means (e.g. mechanical or ultrasonicdispersive procedures). The ferromagnetic material is then recovered bymagnetic means for example with the aid of a magnetic separator or bymagnetic flocculation. If desired, the separated ferromagnetic materialmay be dispersed with a small amount of a suitable liquid and thenrecovered to ensure that particulate matter is not inadvertantlycontained in the ferromagnetic material prior to reuse. Repeatedmagnetisation, and demagnetisation of the ferromagnetic particles is aneffective way of dislodging attached particulate matter.

If the filter aid is magnetised, when used during the filtration cycle,the void volume, and therefore the porosity of the precoat layer, willbe greater than when the filter aid is unmagnetised. It is thereforepossible to regulate the porosity of the precoat by regulating theextent to which the ferromagnetic particles have been magnetised.

In order to obtain a uniform coating on vertical filter septums it isdesirable that the filter aid does not settle too rapidly in the feedslurry. Consequently it is advantageous to use ferromagnetic polymerparticles of the vesicular type in order to reduce their specificgravity and to apply the particles in an unmagnetised state.

In the treatment of sewage with a magnetic filter aid according to ourinvention, the filter cake with the organic particulate matter may beredispersed in a fraction of the circulating liquid stream and theresulting sludge digested. After the organic materials have beendecomposed by bacterial action the filter aid may be recovered from thehumus sludge by magnetic means and reused. Some of the supernatantliquid after the separation of humus sludge can be recirculated forredispersion of the filter aid. Similarly mixtures containing gelatinoushydrated metal hydroxides often encountered in mineral extraction may befiltered easily, using ferromagnetic particles. These particles may bereused.

The problem of removing slicks of oil from water is growing in the worldand concern over the effect of pollution on the ecology of the ocean andthe amenities of its environs is widespread. Many methods of treatingoil slicks have been proposed but these methods merely transfer theproblem to another ecological system. For example it has been proposedto emulsify the oil with a detergent which will of course spread thepollution throughout the body of the water or for example it has beenproposed to sink the oil with heavy mineral powder such as gypsum orstucco, which will pollute the lower levels of the ocean. However, ourinvention may be used to remove oil slicks efficiently and withoutdamage to ecological systems.

Accordingly we provide a method of removing oil slicks from aqueousmedia, said method comprising: firstly, treating said slick withsufficient fine particles or granules of ferromagnetic material beingcharacterised in that said ferromagnetic material preferentially absorbsor adsorbs oil from aqueous media and also the particles or granulesfloat on the aqueous media when associated with the oil; secondlyremoving said particles together with the associated oil by magneticmeans.

Preferably the ferromagnetic material is a synthetic ferromagneticpolymer. The selection of suitable polymers is not narrowly critical andcan be based on the criterion of wettability in the oil phase. Thepolymer should also be insoluble in both the oil phase and the aqueousphase.

Suitable ferromagnetic polymeric materials for use in this aspect of ourinvention include, for example, ferromagnetic particles incorporatedwholly or partially within polystyrene or copolymers of styrene andpolyesters.

The specific gravity of the ferromagnetic polymeric particles may beadjusted by methods known in the art. Ferromagnetic vesicular andretiporous particles are convenient to use as their specific gravity isreadily controlled by methods known in the art.

A magnetic field may be, for example, generated by a boom drawn above orbelow the surface of the water. The particles and associated oil may beremoved from the boom by any suitable mechanical means eithercontinuously or periodically.

A further advantage of using ferromagnetic particles or granules forphase separation is that the force of the magnetic field used forcollecting the said particles or granules is such that it will exertsufficient pressure on the particles or granules for them to assume acompact form without however, squeezing the collected phase from betweenthe particles. A still further advantage of using certain ferromagneticparticles or granules is that after collection the particles or granuleswill be magnetised and will tend to clump together and adhere to anyferromagnetic material. Therefore they may be easily conveyed by meansof ferromagnetic belts or other conveyor means. The particles orgranules may be easily demagnetised by passing them through any suitabledemagnetiser. It is sometimes advantageous to use a soft ferritecontaining polymer as such a polymer may be dispersed more readily so asto facilitate its application to an oil slick, for example, by aspraying technique. Such soft ferrite materials are strongly attractedby a magnetic field and can therefore be collected readily by magneticmeans.

Our invention is also of use in a phase separation problem encounteredin cooling towers. In normal operation of cooling towers water flowsover a packing, or is sprayed countercurrent to an air flow and there isoften a substantial loss of water due to the entrainment of waterdroplets by the exit air stream. This is of course an example of aliquid/gas phase system and suitable hydrophilic ferromagnetic particlesmay be dispersed in the water entering the tower, to allow the air andwater to be separated more efficiently, by increasing the settling rateof the water droplets and to permit their trapping by magnetic means.

Magnetised particles are usually preferred, for use in such a processbecause the void volume, and settling rate of magnetised particles isgreater than that of unmagnetised particles. Magnetised ferromagneticparticles, encapsulated with a polymer are more readily redispersed andare therefore particularly useful.

Accordingly we provide a process of separating liquid and gas phaseswhich process comprises the separation of droplets of a liquidcontaining ferromagnetic materials wettable by said liquid, entrained ina gas stream by magnetic means.

In applying the method to a cooling tower the feed water to the tower isfirst mixed with ferromagnetic particles and the slurry then passedthrough the tower, countercurrent to an air stream. At the base of thetower there is a settling basin where the particles are removed from thecooled water by magnetic means. Spray loss from the tower is reducedbecause the droplets settle more rapidly owing to their containingferromagnetic materials; however any droplets entrained in the exit aircould be recovered by magnetic means. For example, droplets containingsuch magnetic particles in the exit air may be passed over baffles ofpolymers loaded with magnetised particles e.g. barium ferrite andpreferably with water repellant surfaces e.g. a fluorinated hydrocarbon.This attracts the magnetic water particles and thereby reduces losses.The particles accumulate on the surface through the coalescing effect ofthe water film, growing in size until they eventually slide off themagnetic surface. Other magnetic devices may be utilised to facilitateremoval of the water from the magnetic particles.

The particles may be inorganic ferromagnetic materials or ferromagneticmaterials encapsulated by hydrophilic polymers, or encapsulated byhydrophobic polymers with surfaces of a hydrophilic nature graftedthereon.

To these polymeric magnetic particles may be attached algicides or thelike to inhibit slime growth in the tower. The magnetic particles maybe, for example, soft ferrites, hard ferrites or intermediate materialssuch as gamma-iron oxide.

Another phase separation problem which benefits from the use offerromagnetic polymeric particles is the sealing of pipe joints,particularly where a united mobility in such joints is desired, such as,for example, in the sealing of joints in sewerage pipes or gas pipelines. Owing to soil movement it is extremely difficult to preventcracks developing at the joints of underground pipes. Liquids from theground, for example, water, percolate through such joints and this ismost undesirable as in sewage pipes for example it increases the volumeof effluent for disposal or treatment and raises the salinity of theeffluent when the ground water is saline.

We have now discovered that when the surfaces of the joints in pipes aremagnetised and the space between the magnetised surfaces is packed withfinely divided, hydrophobic magnetised particles having surfaces whichare not wetted by water, the magnetic field holds the particles inplace, even when the joints move, and the water repellency of theirvoids prevents entry of water. A refinement is to form a paste havingthe consistency of a grease with the hydrophobic ferromagnetic particlesand an oil which preferentially wets the particles and which is highlyresistant to microbiological attack e.g. fluorinated hydrocarbons orsilicones. The paste is then applied to the magnetic joints.

The magnetic surfaces in the joints may be for example a layer ofmagnetic material either bonded with a cement e.g. portland cement orbonding adhesives stable in the environment.

Accordingly we provide a method of sealing pipes, with a flexible joint,such that fluid may not percolate into or out of the pipe through thesaid joint, said method comprising the use of a sealant comprising acomposition of a finely divided ferromagnetic particles optionally inthe presence of a stable oil, said oil wetting the said particles, andthe use of said sealant in the joints of magnetised pipes whereby themagnetic force of the pipes holds the sealant in place in the joint.

Our process may also be used in the separation of solid and gas phaseswherein the solid phase is separated from a gas phase, for example, theremoval of solid particulate matter from flue gases, by passing themixed phases through a filtration device comprising ferromagneticmaterials.

The process of our invention is also of use in liquid/liquid extraction.When a liquid medium contains a very small concentration of a givenmaterial it is often difficult or expensive to extract efficiently thematerial into a second liquid medium. For example aqueous solutionscontaining metal salts may be treated with complexing agents to formcomplexes such as chelates soluble in non-polar solvents. However in thepast relatively large amounts of non-polar solvent have been required toremove small amounts of complexes because of the difficulty ofseparating the aqueous and organic phases efficiently and the processhas therefrom been expensive for removing trace impurities. We havefound that our process of phase separation may be employed to separatethe phases after a liquid/liquid extraction and particularly when onephase is a small proportion of the whole composition. This embodiment ofour invention has the advantage that by its use trace impurities may beremoved from effluent from chemical, municipal and industrial plantprocess streams and metallurgical operations in an economical manner.

Accordingly in the process of liquid/liquid extraction comprisingextracting a compound from a solution of the compound in a liquid mediumwith a second liquid medium immiscible with the first liquid medium weprovide the improvement consisting of separating the two liquid phasesby firstly adding ferromagnetic particles being characterised in thatsaid ferromagnetic particles preferentially absorb or adsorb the secondliquid medium; and secondary removing said particles together with theassociated second liquid medium by magnetic means. This embodiment ofour invention although for use for separating any proportions of the twoliquid media is of especial use when the second liquid media is only aminor proportion of the total composition, for example less than 10% w/wof total composition.

In order to work a liquid/liquid extraction process efficiently usingsmall proportions of extracting liquid it is desirable for the twoliquids to be mixed together extremely well. This thorough mixing canlead to emulsions which render the prior art methods of separation ofphases extremely inefficient. The process of our invention howeverseparates the constituent phases of emulsions without difficulty.

In order to remove certain compounds from solution it is desirable toadd suitable complexing agents either directly to the first liquidmedium or dissolved in the second liquid medium. The purpose of thosecomplexing agents is to form a complex with the compound which complexhas a more favourable partition coefficient than the compound forextraction by the second liquid medium.

The nature of the complexing agent depends upon the nature of thecompound to be removed. The complexing agent should form a complex withthe compound to be removed. The nature of the second liquid mediumdepends upon the nature of the first liquid medium and also upon theproperties of the complex found between the complexing agent and thecompound to be removed. In liquid/liquid extractions it is desirable forthe two media to be mutually insoluble and for the complex to be freelysoluble in the second liquid medium and sparingly soluble in the firstliquid medium. Suitable combinations of liquid media and complexingagents for liquid/liquid extractions are well known in the art. It ispossible to choose an organic liquid medium which acts both as thesecond liquid medium and as the complexing agent and use of such anorganic liquid medium falls within the scope of our invention.

Although the ferromagnetic particles may be any particles with therequired characteristics we prefer that the ferromagnetic material is asynthetic ferromagnetic polymer.

In liquid/liquid extractions of trace materials from an aqueous solutionwith a non-polar media suitable synthetic ferromagnetic polymers are asdescribed hereinabove as suitable for the removal of oil slicks fromwater. This embodiment of our invention is of particular use in removingsmall amounts of metals salts from the process streams and effluents ofhydrometallurgical mining operations.

Our invention is illustrated in, but not limited by, the followingexamples in which all parts and percentages are by weight unlessotherwise stated and by the accompanying FIG. 1 which provides certaincomparative flow rate data.

EXAMPLE 1

This is an Example of the preparation of a ferromagnetic polymericparticle of use in our invention.

A dispersion of gamma-iron oxide was prepared as follows:

"Bayer S11 gamma-iron oxide" (Trade Mark for a gamma-iron oxide) (51 g.)was added to a solution of 5.1 g. of "Teric PE68" (Trade Mark ofImperial Chemical Industries of Australia and New Zealand Limited for analkylene oxide condensate) in 400 mls of water and stirred vigorouslyuntil the dispersion consisted of clusters of oxide particles smallerthan 5 microns.

A solution of polyvinyl alcohol (491 mls of a 20% solution w/v) and 2 g.of "Gelvatol 20-30" (Trade Mark for a polyvinyl alcohol) was added andthe suspension stirred until it consisted of clusters of oxide particlessmaller than 5 microns.

To the above suspension was added a 25% aqueous solution ofglutaraldehyde (200 mls) and 2 N.HCl (70 ml) with rapid stirring. Thesolution was immediately dispersed into 2 l. of kerosene to which hadbeen added 40 g. of "Span 80" (Trade Mark for sorbitan mono-oleate) and10 g. of "Tween 85" (Trade Mark for a polyoxyethylene sorbitanmono-oleate).

Vigorous stirring was continued for one hour followed by gentleagitation for about 6 hours. The product was filtered off, washed withkerosene, hexane and finally acetone until the filtrate was clear. Theparticles so obtained were dried and cured for 1 hour at 100° C. 170 g.of particles were obtained with an average size of 10 microns andcontaining 60% w/v of gamma-iron oxide.

EXAMPLE 2

This Example demonstrates the ease with which a dispersion offerromagnetic particles may be settled out from a liquid. The particlesobtained in Example 1 (1 g.) were dispersed by shaking with 100 ml. ofwater in a 200 ml stoppered measuring flask. The dispersion took morethan 20 minutes to settle. However, when a similarly prepared dispersionwas held over a strong magnet the dispersion settled in a few seconds.The settled particles were demagnetised in an apparatus described by G.W. Davis (Physics 6 184 (1935)).

The demagnetised particles could be redispersed to yield a compositionhaving the same properties as the initially prepared dispersions. Whenthe magnetised particles were redispersed without demagnetisation, theso formed dispersion settled in a few seconds.

The particles were magnetised and demagnetised many times without damageto the particles.

EXAMPLE 3

This is an example of the preparation of a shell grafted particlesuitable for use in our invention.

The particles (26.7 g.) prepared in Example 1 were added to 100 mls ofstyrene. The mixture was purged with nitrogen and irradiated in anitrogen atmosphere with Cobalt 60 gamma-rays at a dose rate of 0.11 M.Rad/hr. to a total dose of 5.1 M. Rad. The particles were removed andwashed with benzene until free of homopolymer and finally washed withmethanol and dried under reduced pressure at 65° C. 56.4 g. of particleswere obtained containing 52.7% of polystyrene.

EXAMPLE 4

This Example demonstrates the removal of an oil slick from the surfaceof water.

To a 12 inch dish containing 100 ml of water was added 1 ml of crudeoil. The particles (approximately 200 mg.) prepared in Example 3 weredusted over the surface. The particles were wetted by the oil and when amagnet was moved close to the surface of the water the particles andassociated oil were removed leaving an almost clean surface.

EXAMPLE 5

This is an example of destroying an oil slick by burning.

Water (100 ml) and crude oil (1 ml) were placed in a 12 inch dish. Theparticles prepared in Example 3 were magnetised by placing them in astrong magnetic field for a brief time. The magnetised particles soprepared (100 mg) were placed in the centre of the oil slick preparedabove. The oil was attracted towards the small clump of particles. Theparticles formed a wick and the oil was ignited and removed by burning.

EXAMPLE 6

Examples 6 to 9 describe the preparation of vesicular polystyreneparticles of use in our invention.

A mixture of fumaric acid, phthalic anhydride and propylene glycol inthe molar proportions of 3:1:4 respectively, with an acid value of 38and Gardner Holt body Z2 at 70% w/w in styrene was prepared. To thispolyester solution (29.5 lbs.) was added with high speed stirring, 11.8lbs. of styrene, 1 lb. of benzyl peroxide (55% w/w is dibutyl phthalate)and 20 lbs. of "S11 gamma-iron oxide". The mixture was stirred until allthe compounds were well dispersed.

A second mixture was prepared by mixing water (66 lbs.), a 2.25% w/whydroxyethyl cellulose concentrate (8.25 lbs.), "Gelvatol 20/90" (5.5lbs.) (Trade Mark for a polyvinyl alcohol), diethylene triamine (51 g.)and aqueous ammonia s.g. 0.88 (3.74 g.).

The first mixture was added under vigorous stirring by means of a flutedstirrer to the second mixture. More water (110 lbs.) was added and afterflushing with nitrogen the mixture was heated at 90° C for two hourswhen the polymerisation was virtually complete. After polymerisation themixture was diluted 5-fold with water and the particles allowed tosettle, washed by decantation and dried at 105° C. Vesicular particleswere obtained containing an average of 50% void space. The averageparticle size was 15-20 microns.

EXAMPLE 7

Example 6 was repeated except that the gamma-iron oxide of that Examplewas replaced by "Ferrox cube 3E" (Trade Mark for a soft ferrite). Thisis an example of the preparation of a vesicular particle with softferrite properties.

EXAMPLE 8

Example 6 was repeated except that the gamma-iron oxide of that Examplewas replaced by "Black iron oxide 318M" (Trade Mark for a hard ferrite).This is an Example of the preparation of a vesicular particle with hardferrite properties.

EXAMPLE 9

Example 6 was repeated except that only 3 lbs. of styrene was usedinstead of the 11.8 lbs. used in that Example. The particles formed inthis example were of irregular shape.

EXAMPLE 10

This is an example of the removal of oil slicks on water surfaces andthe recovery of the polymer for reuse. Fuel oil (10 mls) was placed in a12 inch dish containing 100 ml of water. Polymer particles (5 g.)prepared in Example 6 were dusted over the oil slick and the contents ofthe dish were vigorously stirred. The particles floated to the top ofthe water associated with most of the oil, and the oil and particleswere removed using a magnet covered with a thin polythene film. Theparticles were separated from the associated oil by vacuum filtrationwhen 7 mls of oil were recovered. The recovered particles were reusedrepetitively to remove fresh oil slicks prepared as above.

EXAMPLE 11

Example 10 was repeated using the particles prepared in Example 7 inplace of the particles prepared in Example 6. Similar results wereobtained as in Example 10 except that as the particles were preparedfrom a soft ferrite it was easier to remove the particles from themagnetic field and also redispersion of recycling the particles waseasier as little permanent magnetism was induced in the particles.

EXAMPLE 12

To an oil slick prepared as in Example 10 there were added the particles(5 g.) prepared in Example 8. The particles were drawn together by amagnet to the centre of the dish forming a clump of particles, heldtogether by magnetic forces. The particles and oil were set on fire andburned until nearly all the oil was removed from the surface, leaving anon-polymeric iron oxide sludge which settled to the bottom of the dish.

EXAMPLE 13

This illustrates the use of a polymer particle for the removal of veryfine droplets of water dispersed in an oil. The particles were preparedas follows.

A mixture of a 25% aqueous solution (4.55 ml) of glutaraldehyde and 2 g.of gamma-iron oxide was added to 50 ml of a 20% w/v aqueous solution of`Gelvatol 20-30`, and after being thoroughly mixed the whole wasacidified by addition of hydrochloric acid (2 N; 2.87 ml). The mixturewas stirred by hand for 15 sec. before being dispersed into droplets byaddition to stirred mineral oil (200 ml; `Ondina 33` Trade Mark of ShellOil Co. Ltd.) at ambient temperature. After continuous mechanicalstirring for 45 minutes, the temperature of the suspension was raisedduring 15 minutes to 70° C and maintained at that level for a further 20minutes. The cross-linked polyvinyl alcohol particles thus formed wereseparated from the cooled mixture, washed with hexane to remove adherentoil, then with acetone and finally with water, in a column, until theeffluent was free from chloride ion and had a pH of 5 or greater. Thewashed product was partially dehydrated by treatment with acetone andfinally dried in vacuo at 50°-60° C. for 24 hrs., to yield hardparticles of cross-linked polyvinyl alcohol in the size range 0.5 - 5microns. The size of the particles within this range was controlled byvarying the stirring speed during their preparation.

When a suspension of fine droplets of water in kerosene was added to thedried beads at room temperature they rapidly absorbed the water. Whenthe beads had absorbed about 50% by weight of water they were fullyswollen. On heating them to 80° C they shrunk and 35% by volume of wateroozed out of the beads and was removed. After the beads were cooled theycould reabsorb water.

When water continued to be added to the fully swollen cold particlesthey joined together as a film of water developed around the particlesand encased them. The swollen particles and associated water wereremoved from the kerosene by means of a magnet covered with polythenefilm. The particles and associated water were removed from the magnet bypulling off the polythene film.

In a comparative experiment particles were prepared by a similar methodbut without using any ferromagnetic material. It was found that althoughthese particles absorbed the water satisfactorily they could not beseparated from the kerosene easily unless the minimum size of theparticles was about 100 microns.

EXAMPLE 14

This Example demonstrates the use of the invention in removing a finesuspension of clay from water.

3 g. of the beads prepared in Example 9 were suspended in water andpoured into a 1 inch glass funnel (porosity 2) on which was placed aclose fitting "Whatman No. 54" (Trade Mark) filter paper to form afilter bed. The beads were unmagnetised.

A bed was formed approximately 1/4 inch deep. Water filtered throughthis bed at a rate of 10 ml per minute under a constant head of 7inches.

A suspension of kaolin in water was prepared by decantation from acoarse suspension. This suspension had a turbidity of 40 Jacksonturbidity units (JTU) which was unchanged when passed through a "WhatmanNo. 54" filter paper. This suspension was filtered through the bed ofthe filter aid. The filtrate was clear.

                  TABLE I                                                         ______________________________________                                        Amount of Suspension                                                                            Turbidity reading                                           filtered          of Filtrate JTU                                             ______________________________________                                        After     50 ml       2.3                                                     "        100 "        2.4                                                     "        150 "        2.7                                                     "        200 "        1.5                                                     ______________________________________                                    

The filtration rate at a steady head of 7 inches fell steadily from 5ml/min. to 0.5 ml/min. after the passage of 300 ml. The results aregiven in Table I.

After completion of the filtration cycle a small slug of filtrate waspassed in the reverse direction through the filter septum so as todislodge the filter cake which was slurried with the filtrate. Thefilter aid was then removed with a magnet, rinsed free of entrappedresidue by reslurrying and magnetic recovery, then demagnetised andreused. The reused filter aid performed as in the previous cycle.

A comparison was made with `Hyflo Supercel` (Trade Mark for adiatomaceous earth).

3 g. of `Hyflo Supercel` was suspended in water and formed a filter bed1/4 inch deep on a "Whatman No. 54" filter paper. A portion of thekaolin suspension prepared above was filtered through the filter bed.

                  TABLE II                                                        ______________________________________                                        Suspension passed Turbidity Readings                                          ______________________________________                                        After     50 ml       5.0 JTU                                                 "        100 "        4.5 JTU                                                 "        200 "        1.5 JTU                                                 ______________________________________                                    

The filtration rate at a head of 7 inches fell steadily from 9 ml/min.to 2 ml/min. after passage of 300 ml. The results are given in Table II.

However, the filter aid could not be cleaned by elutriation because thesettling rate of the `Hyflo Supercel` was too low.

EXAMPLE 15

This Example compares the effect of using the particles prepared inExamples 6 and 9, in a magnetised and unmagnetised state as filter aids;with the effect of using `Hyflo Supercel` and `Celite 545` (Trade Markfor a diatomaceous earth).

The particles prepared in Examples 6 and 9 were magnetised by passingthem briefly through the poles of a large shoe magnet.

Turbid water was prepared by decanting the fine material from asuspension of kaolin and diluting this with tap water to a standardturbidity of 40 Jackson Turbidity Units (JTU). The filter bed was ineach case prepared by the following method. A disc of "Whatman No. 54"filter paper was inserted into a 3 cm. diameter sinter glass tubefilter, porosity 2. The filter aid was dispersed in water, and thedispersion poured onto the filter paper.

Six beds, A, B, C, D, E and F, were prepared of the following materialsrespectively:

    Bed A       2 g `Hyflo Supercel`                                              Bed B       2 g `Celite 545`                                                  Bed C       3 g unmagnetised material prepared                                              in Example 6                                                    Bed D       3 g magnetised material prepared                                                in Example 6                                                    Bed E       3 g unmagnetised material prepared                                              in Example 9                                                    Bed F       3 g magnetised material prepared                                                in Example 9                                                

The magnetised materials formed a deeper bed than the unmagnetisedmaterials.

Samples of the turbid water were filtered through each of the six beds,A, B, C, D, E and F, prepared by the above method, and an average headof 15 cm. was maintained. The filter beds C, D, E and F were back washedusing clean water. After agitation the filter aids were allowed tosettle and the turbid wash water decanted off. After three back washingoperations the filter beds were reused and had unimpaired efficiency. Itwas noted that the magnetised materials had the higher settling rates.The beds, A and B, formed from `Celite` and `Hyflo Supercel` could notbe backwashed in this manner. The rates of filtration and the efficiencyof filtration for each of the six beds are given in Table III.

The results demonstrate that the ferromagnetic particles of ourinvention are superior to `Celite 545` whether they be magnetised orunmagnetised and in comparison to `Hyflo Supercel` they have enhancedfiltration rates and the unmagnetised particles are similar in theirefficiency of removal of turbidity. The ferromagnetic particles of ourinvention have the added advantage that they may be recovered and reusedin phase separation processes whereas the diatomaceous earths cannot beso recovered.

                  TABLE III                                                       ______________________________________                                        Bed A               Bed B                                                     Volume  Time     Turbidity  Time    Turbidity                                 ml      min.     JTU        min.    JTU                                       ______________________________________                                         50      6       6.5        1.2     12                                        100     16       1.7        3.0     14                                        150     24       0.9        4.5     12                                        200     33       0.5        6.2     11                                        250     49       0.5        8.0     12                                        300     65       0.3        10.0    12                                        350     85       0.3        12.2    12                                        BED C               BED D                                                      50      5       8          1.5     7.5                                       100     12       1.5        3.7     6.5                                       150     22       0.5        6.0     8.0                                       200     35       0.5        8.0     8.0                                       250     55       0.3        10.0    9.0                                       300     76       0.2        12.2    8.0                                       400     --       --         17.0    8.5                                       500     --       --         22.7    9.0                                       600     --       --         29.0    9.5                                       BED E               BED F                                                      50      4.0     6.0        4.7     3.5                                       100      9.5     1.0        10.0    2.5                                       150     16.0     0.5        16.0    2.2                                       200     24.0     0.4        24.0    2.0                                       250     37.0     0.2        34.0    1.5                                       300     52.0     0.2        42.0    2.0                                       400     77.0     0.2        63      1.2                                       500     --       --         90      0.7                                       600     --       --         122     0.5                                       ______________________________________                                    

EXAMPLE 16

This Example demonstrates the use of our invention in separating viscoussuspensions formed in chemical processes. A slurry was obtained from apolymerisation reaction. This slurry contained a 5% w/w suspension of4-6 micron cross-linked polyacrylic acid beads in an aqueous reactionmedium comprising linear polymer and other by-products and was highlyviscous. When filtration was attempted, with various grades ofpreviously known filter aids, no more than a few drops could be filteredbefore the filter became blocked each time by a layer of gel on thesurface of the septum. A precoat layer of the particles prepared inExample 6, was formed on a monofilament polypropylene filter cloth (2/2Twill, 68 × 30, 8.5 oz. / sq. yd.) as a bed 0.2 cm. deep, on a filter 23cm² in area. 5.0 g of the particles prepared in Example 6 were suspendedin 25 ml of the resin suspension as body feed. Filtration of thesuspension through the precoated septum then proceeded at the rate of 1ml/min. until the filter cake was dry. The upper layer of filter cakewas resuspended in water and the particles removed from the resin bymagnetic means. By such means it was possible to separate thepolyacrylic acid beads from the dissolved by-products present in theslurry after completion of the polymerisation reaction.

EXAMPLE 17

This example describes the preparation of magnetic particles ofirregular shape and size and comprising an urea formaldehyde resin.

326 g of `black iron oxide` 318M were dispersed by suitable means in 326g of urea formaldehyde syrup ("Mouldrite" A256, Registered Trade Mark ofImperial Chemical Industries of Australia and New Zealand Limited) towhich was added 15 g `Teric` PE68 (Trade Mark of Imperial ChemicalIndustries of Australia and New Zealand Limited for an alkylene oxidecondensate) until the oxide was unagglomerated.

This dispersion was added to 1300 ml ortho-dichlorobenzene with 13 g of`Span` 85 (Trade Mark Imperial Atlas for a polyoxyethylene sorbitanmonooleate) with stirring. Stirring was continued at a constant rate for15 - 30 minutes. 15 ml of 2N. hydrochloric acid were added and the resinwas allowed to gel; 300 ml of ortho-dichlorobenzene were added andstirring continued for 1 hour. Curing was completed under gentleagitation for 12 hours at room temperature. The beads were thenfiltered, ortho-dichlorobenzene was removed by steam distillation andthe beads were dried in an oven at 110° C.

The magnetic particles so obtained were designated FA₁ ; the experimentwas repeated with a different stirring rate to give a preparation ofmagnetic particles designated FA₂.

EXAMPLE 18

The two samples of magnetic particles FA₁ and FA₂ prepared according tothe method of Example 17 were tested using the method described inExample 14. 1.5 g of magnetic particles were suspended in water andpoured into a 1 inch glass funnel with a sintered glass disc (porosity2) on which was placed a close fitting "Whatman No. 54" filter paper toform a filter bed. The bed formed was approximately 1/4 inch deep.

A suspension of kaolin in water was prepared by decantation from acoarse suspension. This suspension had a turbidity of 12.5 Jacksonturbidity units (JTU) which was unchanged when passed through a "WhatmanNo. 54" filter paper. This suspension was filtered through the bed offilter aid under a head of 37.5 cm.

Two filter aids designated FA₁ and FA₂ were tested in the unmagnetisedand magnetised form, (indicated by the prefix D and M respectively) andcompared with `Hyflo Supercel` and `Celite` 503 as filter aids.

FA₁ had an average particle size of 50 - 75 microns and FA₂ had anaverage size of 25 microns. `Celite` 503 had an average particle size of15 microns and `Hyflo Supercel` had an average size of 11 microns.

In FIG. 1 the volume of clay suspension passed through the bed isplotted against time and the average turbidity of the product waterindicated against the curves so obtained. It can be seen from thesecurves that considerably better flow rates were achieved than with thecomparative commercial samples and that the blinding of the bed occurredmuch later.

The magnetised particles form beds with better flow rates than theunmagnetised ones, without substantially reducing the quality of theproduct water.

EXAMPLE 19

This example demonstrates the reuse of filter aids.

The filter aids FA₁ and FA₂ used in Example 18 were removed from thetest apparatus, placed in a glass tube, suspended in 10 mls of water byvigorous shaking and settled by attraction in a magnetic field. Thesupernatent liquid was decanted retaining the filter aid with a magnetheld near the side of the tube. The clean filter aid was then againtested as in Example 18, after passing through a demagnetisation cycle.

The filter aids performed as before giving the same filtrationcharacteristics as previously shown in FIG. 1 for the unrecycled filteraids.

EXAMPLE 20

This example describes a shell grafted filter aid.

A resin prepared by the general method described in Example 17, with aparticle size of 250 micron, was treated as follows.

20 g of resin, 20 ml of 2-vinyl pyridine and 20 ml of methanol wereplaced in a 100 ml round bottom flask fitted with nitrogen inlet andoutlet tubes, the end of the inlet tube dropping into the liquid. Thesample was purged with nitrogen for 5 minutes and then irradiated withgamma rays from a Cobalt 60 source at room temperature at a dose rate of0.3 megarad per hour to a total dose of 6 megarad. The sample afterirradiation was washed with methanol till free of homopolymer. Theresultant resin was then treated with a solution of 20 ml of cetylbromide in 80 ml of ethanol under reflux for 24 hours.

The resin was then filtered, washed with ethanol until free of cetylbromide and dried in vacuo at 60° C overnight.

A resin was obtained which had 1% by weight polyvinyl pyridinium cetylbromide grafted to the surface.

EXAMPLE 21

The ungrafted resin and the shell grafted resin both prepared as inExample 20 were tested by the method described in Example 18 in themagnetised form. The ungrafted resin had no effect and the turbidity ofthe product and feed water were both the same (17.5 JTU). The shellgrafted resin however gave a product water of 3.0 JTU for a feed of 17.5JTU. The flow rate in each case was 100 ml/min.

EXAMPLE 22

Filter aid FA₁ from Example 18 was used both in the magnetised state(M-FA₁) and in the unmagnetised state (D-FA₁) to filter a number ofdifferent waters and effluents and its efficiency was compared withsimilar use of `Celite` 503.

The results are given in Table IV below expressed as the turbidity ofthe product water after 100 ml had passed through the bed under the testconditions set out in Example 18.

                  TABLE IV                                                        ______________________________________                                                                             Flow rate                                                    Feed      Product                                                                              after 100                                Filter              Turbidity Turbidity                                                                            mls in                                   Aid     Type of Feed                                                                              JTU       JTU    mls/min                                  ______________________________________                                        M-FA.sub.1                                                                            Tap water   4.5       0.3    50                                       `Celite`                                                                       503      "         4.5       0.6    10                                       D-FA.sub.1                                                                            Effluent from                                                                             19.6      0.1    40                                               an autoclave                                                                  being used                                                                    for polyvinyl                                                                 chloride                                                                      manufacture                                                           `Celite`                                                                       503      "         19.6      0.7     7                                       M-FA.sub.1                                                                            River water 8.5       0.5    50                                       `Celite`                                                                       503      "         8.5       0.7     9                                       ______________________________________                                    

EXAMPLE 23

The general procedure of Example 1 was repeated to give a resin havingan average particle size of 50-100 microns. 120 g of the product wasslurried with 240 ml of water in a jacketed reactor. Oxygen was passedthrough the stirred slurry while the slurry was irradiated at 5° C for20.5 hours at a dose rate of 0.344 megarad/hr (total dose 7.1 megarad).During the last five minutes of irradiation the oxygen was replaced withnitrogen. A solution of 5.5 g ferrous ammonium sulphate (Fe(NH₄)₂(SO₄)₂.6H₂ O) in 30 ml of water was added immediately and the mixtureallowed to stand for 5 minutes. 75 g of acrylic acid were added quicklyduring which addition the temperature rose from 5° C to 8° C. Themixture was cooled to 5° C and stirred for 1 hour, filtered, washed withwater and dried in vacuo at 60° C. 145.8 g of grafted resin wereobtained which corresponded to 17.7% grafted polyacrylic acid.

The magnetised grafted resin was compared with the magnetised ungraftedresin when used as a filter aid. The results were as shown in Table V.

                  TABLE V                                                         ______________________________________                                                Feed Turbidity                                                                            Product Turbidity                                                                            Flow rate                                  Resin   JTU         JTU            mls/min                                    ______________________________________                                        Magnetised                                                                    ungrafted                                                                             17.5        6.7            50 mls/min                                 Magnetised                                                                    grafted 17.5        3.6            70 mls/min                                 ______________________________________                                    

EXAMPLE 24

This example described the preparation of vesiculated magneticpolystyrene particles having different particle sizes and porosities andsuitable for the removal of oil slicks from water.

The general procedure of Example 6 was repeated using the following foursets of ingredients shown in Table VI to give four samples of resins A,B, C, and D respectively. The polyester solution was as used in Example6.

                  TABLE VI                                                        ______________________________________                                                 Resin                                                                Ingredients                                                                              A        B         C       D                                       ______________________________________                                        Polyester                                                                     solution   72.5 g   72.5 g    72.5 g  72.5 g                                  Styrene    55.5 g   55.5 g    55.5 g  55.5 g                                  `Triten` X45                                                                             --       1.0 g     --      --                                      `Teric` X5 --       --        1.0 g   1.0 g                                   `Topanol` A                                                                              --       --        0.13 g  --                                      Water      228 g    61 g      91.0 g  91.0 g                                  Diethylene-                                                                   triamine   0.57 g   0.57 g    0.57 g  0.57 g                                  `Black Iron                                                                   Oxide` 318M                                                                              61 g     61 g      61 g    61 g                                    NH.sub.3   0.5 g    0.8 g     0.8 g   0.8 g                                   Cumene Hydro-                                                                 peroxide   3.0 g    3.0 g     3.0 g   3.0 g                                   Water      750 g    1000 g    1000 -- 1000 --                                                               1200 g  1200 g                                  Hydroxyethyl                                                                  cellulose  1.0 g    1.0 g     --      1.0 g                                   Methyl cellulose                                                                         --       --        1.0 g   --                                      `Gelvatol` 71/2%                                                              20/90      30.0 g   30 g      30 g    30 g                                    ______________________________________                                    

The resins obtained had the physical characteristics shown in Table VII.

                  TABLE VII                                                       ______________________________________                                                 Average   Density      Porosity                                      Resin    Size      g/ml         %                                             ______________________________________                                        A        30-40 mu  0.45         74                                            B        100 mu    1.09         38                                            C        10-30 mu  0.78         55                                            D        800 -                                                                         1200 mu   0.58         69                                            ______________________________________                                    

EXAMPLE 25

The resins A, B, C and D prepared in Example 24 were tested to determinethe effect of porosity and particle size on oil pick-up efficiency. 20 gof Kuwait crude oil was added to four Petri dishes containing water.After 5 minutes exactly 1 g of each of the resins A, B, C and Dseparately was applied to the oil. A large horse-shoe magnet placedinside a plastic bag was used to attract the resin and associated oil.To make sure all the resin was removed from the oil surface anotherapplication of the magnet in a clean plastic bag was used. The weight ofthe oil picked up was determined. This was expressed as ##EQU1## and thefollowing results were obtained

            Resin A      700                                                              Resin B      415                                                              Resin C      422                                                              Resin D      420                                                  

Similar experiments were carried out for crude oils of differing originsand using both sea and and river water.

The results obtained in these experiments were similar and averagedaround 450.

EXAMPLE 26

This example describes the use of magnetic resin particles to reducewater spray.

A 6 inch diameter tube and six feet in length, closed at the bottom andtop was provided with a nozzle at the bottom and a 1 inch side arm nearthe top. The nozzle was connected to a compressed air supply via aregulating valve.

In the tube was placed 1 litre of tap water and the air turned on to 30psi causing a spray of air and water to rise in the tube. After 30minutes 250 ml of water was lost through the side arm in the form ofspray and mist.

The experiment was repeated but to the water was added 100 g of a resinprepared as in Example 1 with a particle size of 5 microns.

A 4000 gauss horse-shoe magnet was placed with the pole piecesstraddling the side arm. After 30 minutes under the same conditions asused before only 75 mls of water was lost.

EXAMPLE 27

The preparation described in Example 17 was repeated to give a resinhaving a particle size of from 50 to 100 microns. A filter bed wasprepared by precoating a coarse polypropylene screen with the resin to adepth of 0.5 inches. The filter bed was treated with 0.02% by weight of`Primafloc` C5 (Trade Mark for a water soluble cationic polyelectrolyteof the polyamine type). Water obtained from the Yarra River having aturbidity of 10 JTU was filtered through the bed under a gravity head of1.2 feet. The flow rate was initially 0.6 gal/min/ft² and had fallen to0.34 gal/min/ft² after passage of 200 bed volumes. The filtrateinitially had a turbidity of 0.1 JTU and after 200 had a turbidity of0.48 JTU.

The precoat was backwashed, using a magnet to retain the resin andfiltration recommended. The flow rate under the same conditionscommenced at 0.7 gal/min/ft² and gradually fell to 0.27 gal/min/ft²after 400 bed volumes had been filtered.

The turbidity of the product varied between 0.7 and 1.5 JTU.

The precoat was backwashed again, and on replacement gave substantiallythe same results.

This cycle was repeated many times.

EXAMPLE 28

A sample of the shell grafted resin prepared in Example 20 was used as afilter aid to filter sewage. A filter bed was prepared by precoating acoarse polypropylene screen with the shell grafted resin to a depth of0.5 inches. Raw sewage obtained from a sewage plant having a turbidityof 52 JTU was filtered through the bed under a level of 1.2 feet. Theinitial flow rate was 1.2 gals/min/ft² and after 20 bed volumes the flowrate had fallen to 0.12 gals/min/ft² the filtrate obtained had anaverage turbidity of 0.5 JTU and had only 50% of the initial C.O.D.

The bed was backwashed, replaced and reused to give substantially thesame result.

The experiment was repeated using as feedstock the overflow from theprimary sedimentation stage at a sewage plant. The feet had a turbidityof 35 JTU. The initial flow rate was 0.42 gals/min/ft² and after 20 bedvolumes this had fallen to 0.1 gals/min/ft² . The average turbidity ofthe product water was 0.03 JTU. After backwashing and repeatedmagnetisation and demagnetisation of the resin the precoat was replacedand the experiment repeated. Substantially the same results wereobtained. This cycle of operation was repeated many times.

EXAMPLE 29

A liquor derived from biological leaching of copper ore contained 1.0grams per litre of Cu at a pH of 3.5. It was extracted with 0.3 volumesof a 25% solution of 2-hydroxybenzophenoxime in kerosene, which wasembodied in a floc of the synthetic ferromagnetic polymer prepared inExample 24 and designated resin A. The liquor was extracted in acountercurrent system comprising three stages of mixing, separated bythree stages of settling, in which the flocs were transferred bymagnetic means countercurrently to the flow of leach liquor.

The organic extractant attained a concentration of 3.0 grams per litreCu, and was stripped by sulphuric acid in a countercurrent system offour stages, to yield a recycle stream of organic extractant, and asolution of copper sulphate, from which the copper was recovered byelectrolysis.

EXAMPLE 30

An effluent from a petrochemical plant contained 15 ppm of dissolvedcopper and was extracted with 0.05 volumes of an organic extractantcomprising 2-hydroxybenzophenoximes dissolved in kerosene and embodiedin a floc of the synthetic ferromagnetic polymer prepared in Example 24and designated resin D. A single extracting stage reduced the copper inthe effluent to 0.1 ppm. The organic extractant was skimmed from thesurface of the effluent by magnetic means, the copper recovered byextraction and the organic extractant recycled.

We claim:
 1. A process of filtering suspensions of particulate matter ina liquid medium which comprises utilizing, as a filter aid, a bedcomprising magnetized ferromagnetic synthetic polymeric particleswherein the particles are in the size range from 0.5 to 40 micronsoverall diameter.
 2. The process of claim 1 wherein the bed isregenerated for further use by back-washing with water.
 3. A processaccording to claim 1 wherein the ferromagnetic synthetic polymericparticles comprises a polymeric material selected from the groupconsisting of polystyrene, copolymers of styrene and polyesters,polyesters, methyl methacrylate polymers and copolymers, phenolformaldehyde resins, polyvinyl chloride, polyolefines, polyamides,polyvinyl alcohol, urea formaldehyde resins and melamine formaldehyderesins.
 4. A process according to claim 1 wherein the liquid medium ispolar and the synthetic ferromagnetic polymer comprises a ferromagneticparticle incorporated either wholly or partially in a polymeric materialselected from the group consisting of polyvinyl alcohol, ureaformaldehyde resins and melamine formaldehyde resins.
 5. A processaccording to claim 1 wherein the synthetic ferromagnetic particles arevesicular or retiporous.
 6. A process according to claim 1 wherein theferromagnetic synthetic polymer is of the shell graft type.
 7. A processaccording to claim 6 wherein the shell graft comprises an inert core ofpolymer selected from the group consisting of polyvinyl alcohol, ureaformaldehyde resin and melamine formaldehyde resin grafted with a shellof a polymer selected from the group consisting of polyacrylic acid,polyacrylamide, polymethylacrylate and polymers of quaternised aminomonomers.
 8. A process according to claim 1 wherein the liquid medium issewage effluent.
 9. A process according to claim 1 wherein the liquidmedium is industrial effluent.
 10. A process according to claim 1wherein the liquid medium is potable water.
 11. A process according toclaim 10 wherein the water is feedstock for a subsequent Sirothermdesalination process.